A pair of mega dams in construction on the Santa Cruz river’s banks could flood more than 135 square miles of the surrounding region--an area almost twice as big as Buenos Aires--and transform Argentina’s last free-flowing glacial river into a series of brackish pools.

This year’s Living Planet Report shows that populations of animals—including mammals, birds, fish, reptiles, and amphibians—plummeted by 60% between 1970 and 2014. But those living in freshwater are experiencing a far more drastic decline: 83% since 1970.